1. Field of the Invention
The present invention relates to a technique of fluidized-bed granulation, and more particularly, to a technique of granulating substances to be processed by subjecting the substances to a tumbling and fluidizing action by a gas introduced into a processing vessel and a rotor rotating in the processing vessel.
2. Related Art Statement
A fluidized-bed granulating apparatus, for example, that shown in FIG. 3, comprises inlet filters 1, a steam heater 2, a wind chamber 3, a lift-up device 4, a wagon 5, a wire mesh 6, a container 7, a spraying chamber 8, a spray nozzle 9, bag filters 10, a shaking device 11, a shaking cylinder 12, a damper 13 for stopping ventilation, and a cylinder 14 for stopping ventilation. However, it is difficult to obtain product having high bulk density with this sort of apparatus because powdered or granular substances in the container are subjected to a fluidizing action only by the gas from the wind chamber 3.
Therefore, in order to solve this problem, a method employing a fluidized bed with rotor disk to obtain spherical and hard product having high bulk density has been known, and an apparatus of this type has been used actually. In such an apparatus, however, a circular slit which is formed between the inner wall of the container and the periphery of the rotor can be closed by, for example, a seal provided around the periphery of the rotor or a vertically movable seal ring provided under this circular slit, so that raw materials do not fall under the rotor from the circular slit when the damper is fully closed to stop ventilation temporarily for the purpose of facilitating the shaking off dust from the bag filters.
In the above-described structure, however, the container or the seal ring is brought into contact with the rotor or the seal, and the rotation of the rotor must therefore be stopped temporarily. Therefore, the effect of the centrifugal tumbling action of the rotor is reduced by half.
In order to prevent the raw materials from falling from the rotor through this slit, it has been proposed to provide the apparatus with a pulse jet cleaning device which does not necessitate the stopping of ventilation temporarily during the removal of dust, or the bag filters are divided into two chambers and a mechanism providing alternate shaking is provided. Since this apparatus is always ventilated, the slit need not to be fully closed. Therefore, the rotation of the rotor need not be stopped, but there is a disadvantage in that the raw materials are not readily subjected to the tumbling action of the rotor because they are always in a fluid state.
Therefore, if an intensive tumbling action is expected from rotating of the rotor, a method could be conceived in which no ventilating portion is provided in the rotor, and the rotor serves as a blind so that only the slit is ventilated and the raw materials are not fluidized but are made to tumble on the rotor. The inventors have found that this method has disadvantages in that, since the amount of hot air used is small and the speed of drying is low, the spraying of a given amount of a binder requires a long time, lumps are produced during the granulation, owing to excess of water in the raw materials, and drying requires another drying machine.